Since 1945, and particularly in the 50's and 60's, there have been efforts to develop a cellular ceramic building material from abundant natural resources, with apparatus and methods for continuous production. The cellular glass blocks on the market since about 1945 initially looked like an acceptable material, but had some drawbacks, including practically no value for protection from fire, and the shapes being extremely friable. Further, the starting material for cellular glass blocks is a borosilicate glass, which is an expensive raw material. This results in a prohibitive cost for heavier and more rugged building blocks.
Certain raw materials, including clays and sands, may be used that are less expensive and found in various areas of the surface of the earth. Other less expensive materials such as fly ash produced as a by-product of manufacturing facilities, from the burning of coal, and trash may be considered and mixed in certain proportions. These cheaper materials may be used to form ceramic blocks, slabs and timbers; however, they require containers of a lesser temperature resistance than the metal alloys used for existing cellular glass blocks. In order to achieve economies of scale and incur minimal material handling costs, materials may be processed in very large quantities requiring significant amounts of heat generation. The existing tunnel kilns used for processing of such materials into ceramic blocks recuperate heat from the flue gas and from the burden (the ware plus the means of containing and supporting in the heat). Presently, the primary air for combustion is brought to the burner at ambient temperature, and a large portion of the fuel consumption is for heating the air to the flame temperature. This leads to large energy consumption costs during the forming process. If the air were introduced into the burner at a high temperature, it would ignite prematurely and unsafely.
One attempt to form cellular blocks is described in U.S. Pat. No. 4,212,635. This patent describes a process in which clay or silica can be mixed with a small amount of soluble carbonaceous material and water to adjust the carbon and moisture content of the clay or silica with the carbonaceous material and water. This mixture is then fired in a kiln to produce a cellulated vitreous refractory material. We have found it difficult to produce suitable product using the teachings of this patent. For example, when using bentonite we had to make a number of changes to the process described in this patent in order to form suitable product, including but not limited to changes in the formulation and changes in the manner in which the formulation is mixed, dried and fired in order to produce a suitable closed cell ceramic material product.